Niobium suboxide is a kind of ceramic material. Due to its metal conductivity, the Nb2O5 dielectric oxide film can be formed on the surface thereof, so electrolytic capacitor can be manufactured thereof.
The agglomerated niobium suboxides powders for manufacturing electrolytic capacitor shall have low content of impurities, large specific surface area, large pore size and good flowability.
There are some available techniques which can be utilized for preparing the powder of niobium suboxides and niobium as mentioned above. But some disadvantages are presented in different aspects.
Chinese patent application CN 1587066A discloses a process for preparing niobium suboxide powders by heat treating the mixture of niobium oxide and capacitor grade niobium powder, in which process the niobium suboxides were prepared through the oxidization of capacitor grade niobium powder by niobium oxide. The problem of this process is that capacitor grade niobium powders have to be prepared in advance. Moreover, after niobium oxide oxidizes capacitor grade niobium powder, some oxygen is lost, the residue is not suitable for manufacturing capacitor. As a result, the period of the process is long. In addition, since the requirements on the capacitor grade niobium powder as starting material are rigorous, this process is not suitable for the industrial scale production.
WO 00/15555 discloses a process, which includes reducing the niobium pentoxide in the presence of hydrogen gas by using the flake, particulates or powder of tantalum or niobium for sufficient time and at a sufficient temperature, which permits the transfer of oxygen atoms from the pentoxides to the reducing agent to reduce niobium pentoxide. This process has some problems as follows: tantalum or niobium in the shape of flake or particulate is used for reducing agent, thus the surface area is low and the contacting area with the oxides is low. As a result, the reaction dos not proceed uniformly, which leads to the distribution of oxygen in the product not uniform, degrading the properties of the product. Since the reducing agent of tantalum or niobium is not soluble in acid, the residue of tantalum or niobium can not be removed.